Hall sensor Bosch/Buderus HS04, 20491109

This Hall sensor, listed under catalogue article 225.208.004 and manufacturer codes 20491109 / 225.208.004, is a sensor component from Bitron. The part is designated Bosch/Buderus HS04, indicating a specific variant used in burner or boiler control systems. A Hall sensor of this type detects magnetic field changes, typically from a rotating magnet on a fan impeller or a magnet ring on a modulating motor shaft. The sensor outputs a pulsed signal that the control board uses to monitor fan speed, confirm airflow, or determine the position of a modulating actuator. This feedback is essential for the correct sequencing of pre-purge, ignition, and modulation in burners of this class. Selection of a replacement Hall sensor depends on the output signal type (normally an open-collector frequency signal), supply voltage (commonly 5 V or 24 V DC), number of poles per revolution, connector format, and cable length. When replacing, verify the air gap between the sensor face and the magnet – an incorrect gap or misalignment will cause erratic pulsing or no signal. Also check that the sensor is securely mounted and that the wiring matches the original polarity. Clean the sensor tip of any metallic debris before installation.